<title>最小差值生成树</title><link href="http://hzoi.com/tomorrow.css" rel="stylesheet"><div class="ui existing segment"><pre><code><span class="pl-cp">#include</span> <span class="pl-cpf">&lt;algorithm&gt;</span><span class="pl-cp"></span>
<span class="pl-cp">#include</span> <span class="pl-cpf">&lt;cstdio&gt;</span><span class="pl-cp"></span>
<span class="pl-cp">#include</span> <span class="pl-cpf">&lt;cstring&gt;</span><span class="pl-cp"></span>
<span class="pl-cp">#include</span> <span class="pl-cpf">&lt;iostream&gt;</span><span class="pl-cp"></span>
<span class="pl-cp">#define ll long long</span>
<span class="pl-k">using</span> <span class="pl-k">namespace</span> <span class="pl-n">std</span><span class="pl-p">;</span>

<span class="pl-n">ll</span> <span class="pl-nf">read</span><span class="pl-p">()</span> <span class="pl-p">{</span>
    <span class="pl-n">ll</span> <span class="pl-n">x</span> <span class="pl-o">=</span> <span class="pl-mi">0</span><span class="pl-p">,</span> <span class="pl-n">w</span> <span class="pl-o">=</span> <span class="pl-mi">1</span><span class="pl-p">;</span>
    <span class="pl-kt">char</span> <span class="pl-n">ch</span> <span class="pl-o">=</span> <span class="pl-n">getchar</span><span class="pl-p">();</span>
    <span class="pl-k">for</span> <span class="pl-p">(;</span> <span class="pl-n">ch</span> <span class="pl-o">&gt;</span> <span class="pl-sc">&#39;9&#39;</span> <span class="pl-o">||</span> <span class="pl-n">ch</span> <span class="pl-o">&lt;</span> <span class="pl-sc">&#39;0&#39;</span><span class="pl-p">;</span> <span class="pl-n">ch</span> <span class="pl-o">=</span> <span class="pl-n">getchar</span><span class="pl-p">())</span>
        <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-n">ch</span> <span class="pl-o">==</span> <span class="pl-sc">&#39;-&#39;</span><span class="pl-p">)</span> <span class="pl-n">w</span> <span class="pl-o">=</span> <span class="pl-o">-</span><span class="pl-mi">1</span><span class="pl-p">;</span>
    <span class="pl-k">for</span> <span class="pl-p">(;</span> <span class="pl-n">ch</span> <span class="pl-o">&gt;=</span> <span class="pl-sc">&#39;0&#39;</span> <span class="pl-o">&amp;&amp;</span> <span class="pl-n">ch</span> <span class="pl-o">&lt;=</span> <span class="pl-sc">&#39;9&#39;</span><span class="pl-p">;</span> <span class="pl-n">ch</span> <span class="pl-o">=</span> <span class="pl-n">getchar</span><span class="pl-p">())</span> <span class="pl-n">x</span> <span class="pl-o">=</span> <span class="pl-n">x</span> <span class="pl-o">*</span> <span class="pl-mi">10</span> <span class="pl-o">+</span> <span class="pl-n">ch</span> <span class="pl-o">-</span> <span class="pl-sc">&#39;0&#39;</span><span class="pl-p">;</span>
    <span class="pl-k">return</span> <span class="pl-n">x</span> <span class="pl-o">*</span> <span class="pl-n">w</span><span class="pl-p">;</span>
<span class="pl-p">}</span>

<span class="pl-k">const</span> <span class="pl-n">ll</span> <span class="pl-n">maxn</span> <span class="pl-o">=</span> <span class="pl-mi">1000100</span><span class="pl-p">;</span>
<span class="pl-n">ll</span> <span class="pl-n">fa</span><span class="pl-p">[</span><span class="pl-n">maxn</span><span class="pl-p">];</span>

<span class="pl-k">struct</span> <span class="pl-n">node</span> <span class="pl-p">{</span>
    <span class="pl-n">ll</span> <span class="pl-n">u</span><span class="pl-p">,</span> <span class="pl-n">v</span><span class="pl-p">,</span> <span class="pl-n">w</span><span class="pl-p">;</span>
    <span class="pl-kt">bool</span> <span class="pl-k">operator</span><span class="pl-o">&lt;</span><span class="pl-p">(</span><span class="pl-k">const</span> <span class="pl-n">node</span> <span class="pl-o">&amp;</span><span class="pl-n">x</span><span class="pl-p">)</span> <span class="pl-k">const</span> <span class="pl-p">{</span> <span class="pl-k">return</span> <span class="pl-n">w</span> <span class="pl-o">&lt;</span> <span class="pl-n">x</span><span class="pl-p">.</span><span class="pl-n">w</span><span class="pl-p">;</span> <span class="pl-p">}</span>
<span class="pl-p">}</span> <span class="pl-n">a</span><span class="pl-p">[</span><span class="pl-n">maxn</span><span class="pl-p">];</span>

<span class="pl-n">ll</span> <span class="pl-nf">find</span><span class="pl-p">(</span><span class="pl-n">ll</span> <span class="pl-n">x</span><span class="pl-p">)</span> <span class="pl-p">{</span>
    <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-n">fa</span><span class="pl-p">[</span><span class="pl-n">x</span><span class="pl-p">]</span> <span class="pl-o">==</span> <span class="pl-n">x</span><span class="pl-p">)</span> <span class="pl-k">return</span> <span class="pl-n">x</span><span class="pl-p">;</span>
    <span class="pl-k">return</span> <span class="pl-n">fa</span><span class="pl-p">[</span><span class="pl-n">x</span><span class="pl-p">]</span> <span class="pl-o">=</span> <span class="pl-n">find</span><span class="pl-p">(</span><span class="pl-n">fa</span><span class="pl-p">[</span><span class="pl-n">x</span><span class="pl-p">]);</span>
<span class="pl-p">}</span>

<span class="pl-n">ll</span> <span class="pl-n">n</span><span class="pl-p">,</span> <span class="pl-n">m</span><span class="pl-p">,</span> <span class="pl-n">maxx</span><span class="pl-p">;</span>
<span class="pl-kt">int</span> <span class="pl-nf">main</span><span class="pl-p">()</span> <span class="pl-p">{</span>
    <span class="pl-n">n</span> <span class="pl-o">=</span> <span class="pl-n">read</span><span class="pl-p">(),</span> <span class="pl-n">m</span> <span class="pl-o">=</span> <span class="pl-n">read</span><span class="pl-p">();</span>
    <span class="pl-k">for</span> <span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">i</span> <span class="pl-o">=</span> <span class="pl-mi">1</span><span class="pl-p">;</span> <span class="pl-n">i</span> <span class="pl-o">&lt;=</span> <span class="pl-n">m</span><span class="pl-p">;</span> <span class="pl-n">i</span><span class="pl-o">++</span><span class="pl-p">)</span> <span class="pl-p">{</span>
        <span class="pl-n">a</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">].</span><span class="pl-n">u</span> <span class="pl-o">=</span> <span class="pl-n">read</span><span class="pl-p">();</span>
        <span class="pl-n">a</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">].</span><span class="pl-n">v</span> <span class="pl-o">=</span> <span class="pl-n">read</span><span class="pl-p">();</span>
        <span class="pl-n">a</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">].</span><span class="pl-n">w</span> <span class="pl-o">=</span> <span class="pl-n">read</span><span class="pl-p">();</span>
    <span class="pl-p">}</span>
    <span class="pl-kt">int</span> <span class="pl-n">ans</span> <span class="pl-o">=</span> <span class="pl-mh">0x7f7f7f7f</span><span class="pl-p">;</span>
    <span class="pl-n">sort</span><span class="pl-p">(</span><span class="pl-n">a</span> <span class="pl-o">+</span> <span class="pl-mi">1</span><span class="pl-p">,</span> <span class="pl-n">a</span> <span class="pl-o">+</span> <span class="pl-mi">1</span> <span class="pl-o">+</span> <span class="pl-n">m</span><span class="pl-p">);</span>
    <span class="pl-k">for</span> <span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">i</span> <span class="pl-o">=</span> <span class="pl-mi">1</span><span class="pl-p">;</span> <span class="pl-n">i</span> <span class="pl-o">&lt;=</span> <span class="pl-n">m</span><span class="pl-p">;</span> <span class="pl-n">i</span><span class="pl-o">++</span><span class="pl-p">)</span> <span class="pl-p">{</span>
        <span class="pl-k">for</span> <span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">j</span> <span class="pl-o">=</span> <span class="pl-mi">1</span><span class="pl-p">;</span> <span class="pl-n">j</span> <span class="pl-o">&lt;=</span> <span class="pl-n">n</span><span class="pl-p">;</span> <span class="pl-n">j</span><span class="pl-o">++</span><span class="pl-p">)</span> <span class="pl-n">fa</span><span class="pl-p">[</span><span class="pl-n">j</span><span class="pl-p">]</span> <span class="pl-o">=</span> <span class="pl-n">j</span><span class="pl-p">;</span>
        <span class="pl-kt">int</span> <span class="pl-n">mn</span> <span class="pl-o">=</span> <span class="pl-n">a</span><span class="pl-p">[</span><span class="pl-n">i</span><span class="pl-p">].</span><span class="pl-n">w</span><span class="pl-p">,</span> <span class="pl-n">maxx</span> <span class="pl-o">=</span> <span class="pl-mi">0</span><span class="pl-p">,</span> <span class="pl-n">cnt</span> <span class="pl-o">=</span> <span class="pl-mi">0</span><span class="pl-p">;</span>
        <span class="pl-k">for</span> <span class="pl-p">(</span><span class="pl-kt">int</span> <span class="pl-n">j</span> <span class="pl-o">=</span> <span class="pl-n">i</span><span class="pl-p">;</span> <span class="pl-n">j</span> <span class="pl-o">&lt;=</span> <span class="pl-n">m</span><span class="pl-p">;</span> <span class="pl-n">j</span><span class="pl-o">++</span><span class="pl-p">)</span> <span class="pl-p">{</span>
            <span class="pl-kt">int</span> <span class="pl-n">xx</span> <span class="pl-o">=</span> <span class="pl-n">find</span><span class="pl-p">(</span><span class="pl-n">a</span><span class="pl-p">[</span><span class="pl-n">j</span><span class="pl-p">].</span><span class="pl-n">u</span><span class="pl-p">),</span> <span class="pl-n">yy</span> <span class="pl-o">=</span> <span class="pl-n">find</span><span class="pl-p">(</span><span class="pl-n">a</span><span class="pl-p">[</span><span class="pl-n">j</span><span class="pl-p">].</span><span class="pl-n">v</span><span class="pl-p">);</span>
            <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-n">xx</span> <span class="pl-o">==</span> <span class="pl-n">yy</span><span class="pl-p">)</span> <span class="pl-k">continue</span><span class="pl-p">;</span>
            <span class="pl-n">fa</span><span class="pl-p">[</span><span class="pl-n">xx</span><span class="pl-p">]</span> <span class="pl-o">=</span> <span class="pl-n">yy</span><span class="pl-p">;</span>
            <span class="pl-n">cnt</span><span class="pl-o">++</span><span class="pl-p">;</span>
            <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-n">cnt</span> <span class="pl-o">==</span> <span class="pl-n">n</span> <span class="pl-o">-</span> <span class="pl-mi">1</span><span class="pl-p">)</span> <span class="pl-p">{</span>
                <span class="pl-n">maxx</span> <span class="pl-o">=</span> <span class="pl-n">a</span><span class="pl-p">[</span><span class="pl-n">j</span><span class="pl-p">].</span><span class="pl-n">w</span><span class="pl-p">;</span>
                <span class="pl-k">break</span><span class="pl-p">;</span>
            <span class="pl-p">}</span>
        <span class="pl-p">}</span>
        <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-n">maxx</span> <span class="pl-o">==</span> <span class="pl-mi">0</span><span class="pl-p">)</span> <span class="pl-k">break</span><span class="pl-p">;</span>
        <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-n">maxx</span><span class="pl-p">)</span> <span class="pl-n">ans</span> <span class="pl-o">=</span> <span class="pl-n">min</span><span class="pl-p">(</span><span class="pl-n">ans</span><span class="pl-p">,</span> <span class="pl-n">maxx</span> <span class="pl-o">-</span> <span class="pl-n">mn</span><span class="pl-p">);</span>
    <span class="pl-p">}</span>
    <span class="pl-k">if</span> <span class="pl-p">(</span><span class="pl-n">ans</span> <span class="pl-o">==</span> <span class="pl-mh">0x7f7f7f7f</span><span class="pl-p">)</span> <span class="pl-n">ans</span> <span class="pl-o">=</span> <span class="pl-o">-</span><span class="pl-mi">1</span><span class="pl-p">;</span>
    <span class="pl-n">cout</span> <span class="pl-o">&lt;&lt;</span> <span class="pl-n">ans</span> <span class="pl-o">&lt;&lt;</span> <span class="pl-n">endl</span><span class="pl-p">;</span>
<span class="pl-p">}</span>
</cpde></pre></div>